My friend has a 2 bedroom apartment on Alvarez Thomas y Concepción Arenal. I'll have to make sure it is still available... You may not be interested since it is a 2 bedroom, but who knows maybe you'll find a roommate. He'd prefer to do a 6 month contract, but he'd consider other offers. He's asking U.S. $650/month for up to two people staying in it, more if it is more than 2 people. The place isn't anything incredible, but decent. I've got pictures and more details if you want them.
i hope the links can help you out. I just have to move out from my place and i found a very nice room, internet, AC, just a block from subte and buses for 600 pesos (i share a flat with one more person)! If you want a room in Palermo, Recoleta, Sant Telmo is more expensive!!